ISOTHERMAL DIFFUSION-COEFFICIENTS OF NACL-MGCL2-H2O AT 25-DEGREES-C .5. SOLUTE CONCENTRATION RATIO OF 1 1 AND SOME RAYLEIGH RESULTS/

Isothermal interdiffusion coefficients have been obtained by Gouy inte rferometry for the ternary system NaCl-MgCl2-H2O at 25.00-degrees-C an d a 1:1 mole ratio of NaCl to MgCl2. Data are reported for total molar concentrations of 0.5, 1.0, 2.0, 3.0, and 3.72 M. Diffusion coefficie nts at mole ratios of 1:1 (0.5 and 1.0 M), 1:3 (1.0 and 3.0 M), and 3: 1 (1.0 M) were also obtained by Rayleigh interferometry during the cor responding Gouy experiments by switching the two optical systems back and forth. As expected, good agreement is found between Gouy and Rayle igh results. Diffusion coefficients at the 1:1 ratio are intermediate between the results for 1:3 and 3:1 ratios, with D12 becoming large wi th increasing concentration but always less than D11 and D22, and with D11 and D22 crossing at 2.8 M. Densities were measured for all soluti ons. Rayleigh experimental and data analysis techniques are described.